In greenhouse corn production, artificial light sources, such as high intensity discharge (HID) lamps, are extensively applied to provide higher light intensity at plant canopy. Traditionally, these HID lamps are installed on a light frame that is maintained at a fixed distance from the plant growing area. This arrangement does not compensate for changes in light intensity due to plant development or changes in light intensity due to weather or seasonal conditions. When plants are at younger stages, the distance between the lights and plant canopy is larger, and the light intensity at the plant canopy is lower; when plants have developed to more advanced stages, the distance between the lights and plant canopy is smaller, and the light intensity at plant canopy is higher. Weather and seasonal changes also introduce variation in light intensity at plant canopy. These variations in lighting conditions are not desirable, because they may introduce abiotic stress on the plants, and thus lead to variation in the quantity and quality of the final yield.